Engines may use various cylinder intake and/or exhaust valve profiles to improve engine operation over a range of conditions. For example, engines may use variable valve timing, cam profile switching, and others to provide different valve operation. Switches between the different valve profiles are typically controlled via hydraulic circuits, which may have variable delays. These delays can result in valve operation different than that desired for a given combustion event.
One approach considering the delay of an oil circuit for changing valve characteristics is described in U.S. Pat. No. 6,330,869 where the combustion before and after the changeover of valve operation is a spark ignited combustion. In this reference, the property of the working oil in the hydraulic valve characteristic changing mechanism of the valve moving apparatus is detected, and the delay time is altered in accordance with the detected property of the working oil to make a change of the valve operation coincide with the change of the combustion condition of the engine.
However, the inventors herein have recognized disadvantages with such an approach, especially when applied to an engine changing combustion modes during the switch in valve operation, such as between a spark ignition combustion and a compression ignition combustion.
Specifically, there are numerous factors that may affect the valve switching and combustion modes. For example, the time delay may include factors such as delays in the electronic and solenoid valves. In addition, external conditions such as humidity or altitude may affect the response time of the tappet switch order required for transitioning combustion modes between different combustion modes, such as spark and compression ignition. Finally, errors in tappet switching may result in undesired combustion modes in cylinders and may cause engine misfires in a compression ignition mode, for example.
Thus, in one approach, the above issue may be addressed by a method of controlling cylinder valve switching between a first valve condition and a second valve condition for transitioning between combustion modes of an engine. The method comprises adjusting timing of a signal to switch between said valve conditions in response to information from a combustion sensor, wherein said combustion modes include spark ignition and homogeneous charge compression ignition.
In this way, it is possible to compensate for dynamics of the oil circuit and the delay in electronic components via combustion sensor information. Thus, it is possible to provide accurate control of a valve switching order during transition of combustion modes, thereby reducing torque fluctuations, emission spikes, vibration and audible noise. In one embodiment, information as to the timing of when each tappet has switched may be used to provide appropriate signal timing so that the correct amount of fuel can be injected into the respective cylinder, and the required temperature and pressure can be achieved inside the cylinder to perform desired combustion modes such as HCCI and SI.
Furthermore, learned modifications to the switching time and/or order may be achieved enabling adaptation over time based on information from a combustion sensor to account for system degradation as well as external conditions such as humidity or altitude.